Once, the people of the City invited Mulla Nasruddin to deliver a khutba (public lecture).
When he got on the minbar (pulpit), he found the audience was not very enthusiastic, so he asked "Do you know what I am going to say?"
The audience replied "NO", so he announced "I have no desire to speak to people who don't even know what I will be talking about" and he left.
The people felt embarrassed and called him back again the next day. This time when he asked the same question, the people replied "YES" So Mullah Nasruddin said, "Well, since you already know what I am going to say, I won't waste any more of your time" and he left.
Now the people were really perplexed. They decided to try one more time and once again invited the Mullah to speak the following week.
Once again he asked the same question - "Do you know what I am going to say?" Now the people were prepared and so half of them answered "YES" while the other half replied "NO".
So Mullah Nasruddin said "The half who know what I am going to say, tell it to the other half" and he left!